The present invention relates to an optical recording system for recording an image with light, or more in particular to a system and a method for controlling the quantity of light.
In recording an image including characters, a figure or even a natural scene like a photograph by a digital recording system, the first step is to sample and quantize the particular image. An image input unit of an image scanner or the like forms a plurality of meshes numbering, say, 16 per millimeter in each of x and y directions on an image. The point making up each mesh is called a pixel and is used as a minimum spatial unit. The term "spatial" is associated with a two-dimensional expansion along the x and y directions. The image input unit generates pixel data representing the image density in a pixel (Sampling). This pixel data, which normally assumes an analog value, is converted into a digital value like an eight-bit binary data by A/D conversion means (Quantization). An optical recording system for recording such an image made up of image data is configured, for example, as shown in FIGS. 25 and 26.
A configuration of a machine unit (engine) generally used with an optical recording system is shown in FIG. 25. The recording mainly requires the following processes:
______________________________________ (1) Charging: To charge a light-sensitive material uniformly (2) Exposure: To expose to light to form an electrostatic latent image (3) Development: To cause the latent image to adsorb a developer to make a visible image (4) Transfer: To transfer the adsorbed developer to the recording paper (5) Fixing: To fuse and fix the developer on the recording paper (that is, a recording medium) (6) Erasure: To remove the static electricity remaining on the light-sensitive material (7) Cleaning: To clean off the developer from the light-sensitive material ______________________________________
FIG. 26 shows only the exposure of all the processes shown in FIG. 25. This process is operated generally in the manner described below.
A modulation circuit 55 converts image data (printing information) into an electrical signal and produces a modulated electrical signal, which signal is used to drive a laser beam source 54 thereby to produce a laser beam 51. The laser beam 51 scans while being irradiated on a light-sensitive material drum 50 through a mirror 52 rotated by a motor 53. In this optical recording system, attention is paid only to the pixel data to be recorded Specifically, this data is appropriately corrected and the exposure amount on the light sensitive material is modulated for recording purposes on the basis of the pixel data thus corrected. The recording of the same pixel data, however, is known to require different methods of correction or modulation for recording a high-quality image depending on what kind of image the particular pixel data belongs to in the whole picture. In the case of reversal development for monochromatic binary recording using a laser printer to record the exposed surface portion of the light-sensitive material in black color and the unexposed portion thereof in white color, for example, the black pixels for recording a large black area (hereinafter called "the solid image") and those of other lines or characters must be processed in different ways if a high-quality recording is to be achieved. Let us apply this idea to the laser printer using the reversal phenomenon in a system disclosed by JP-A-62-26621. In the case where the pixels above and below the black pixels to be recorded (hereinafter called "the recording black pixels") are black, the surface of the light-sensitive material corresponding to the recording black pixels is exposed with greater intensity in recognition of the fact that the recording black pixels are those included in a solid image. This increases the diameter of the recording dots corresponding to the size of the recording per beyond a prescribed value and therefore white portions in the solid image caused by irregular intervals of beam scannings are removed, thereby making it possible to record a high-quality solid image. In the case where the pixels above or below the black pixels to be recorded are white, on the other hand, the black pixels to be recorded are recognized to be those within lines or characters, and thus are exposed less intensely so that the diameter of the recording dots is identical to a prescribed size. In this way, the quantity of the laser light emitted is controlled for each pixel to improve the quality of the solid image portion without adversely affecting the image quality of lines or characters, resulting in a high-quality recording of the particular image as a whole.
A host system including a work station or a word processor produces and applies toward a recording system pixel data generally sampled and quantized by a standard method. This quantized pixel data takes such a form as a language including a postscript or a command standardized according to JIS or the like or data compressed by an MH method or the like. In any case, this data is restored to the normal pixel data (raw data). An attempt to use such an image data in direct form, however, would fail to utilize the full performance of a recording system as the recording characteristics vary from one recording system to another and the result would be an unsatisfactory utilization of the functions or a recording failure of the particular recording system. The recording characteristics of a light recording system such as the laser printer or the LED printer include, for example:
(1) The light quantity is controlled continuously in either a main or a subsidiary scanning direction, but discretely with a predetermined density in the other direction for the purpose of recording. PA1 (2) The diameter of the recording dot by the laser beam light varies with the amount of exposure from the light source to the light-sensitive material (which amount may hereinafter be called "the exposure pattern" or if expressed by an electrical signal, "the light pattern signal").
As a result, unless the standard image data from the host system is corrected and modulated taking these characteristics into consideration before recording, it is impossible for the optical recording system to display its maximum performance. The aforementioned related art system, which is intended to record the solid image portion in a stable manner by taking advantage of the characteristic (2) above, fails to pay due attention to straight lines having a given inclination or intersections, fine stripes or checkers, or screen dots included in a half-tone image or the like.
Also, the aforementioned system fails to utilize the other characteristic (1), and thus the performance of the optical recording system is not fully exhibited.